As is conventionally well known, intake systems are improved in the charging efficiency of intake air by making use of pressure waves caused to the dynamic characteristics of intake air such as intake inertia, resonance and so forth so as to obtain an increased generating power of a vehicle engine. Such intake systems are inevitably made bulky or oversized, not only because of the necessity of providing a surge tank as means for reversing negative pressure waves caused in the intake system and conducting the reversed pressure waves into a combustion chamber of such cylinder of the vehicle engine, but because of the necessity of a sufficient length of intake pipe in order to conduct timely the reversed pressure waves from said pressure reversing means into the combustion chamber of the cylinder.
In an attempt at overcoming the drawbacks associated with the above-described intake systems, an intake system for a V-type vehicle engine is disclosed in, for example, U.S. Pat. No. 4,649,871 entitled Intake System For V-Type Engine issued on Mar. 17, 1987 and assigned to the same asignee as the present invention. The intake system taught by the U.S. Pat. No. 4,649,871 has intake passages for engine cylinders in each cylinder bank which first extend from the side of a surge tank remote from the cylinder bank toward the other cylinder bank and then are bent toward the cylinder so that the intake passages for both the cylinder banks cross one another below the surge tank. Each intake passage for the cylinders in each cylinder bank comprises a U-shaped bight portion which projects from the side of the surge tank remote from the cylinder bank toward the other cylinder bank and is bent toward the cylinder bank, and a crossing portion which is connected between the corresponding intake port in the cylinder bank and the downstream end of the U-shaped bight portion and crosses the intake passages for the cylinders in the other cylinder bank below the surge tank.
A drawback associated with the above-described intake system is not only that, because the surge tanks are arranged side by side in the transverse direction of the vehicle engine, and it is difficult to make use of a large cross sectional area of surge tank, but that, because of the large curvature of the intake passages, intake air is subjected to an increased resistance, resulting in the difficulty of taking in a large quantity of air in a high speed operating range of engine. In order to allow the provision of a large cross sectional area of surge tank and a reduced curvature of intake passages, it is unavoidable to increase the overall height of the vehicle engine. However, because engines with intake systems are located below a hood, the intake systems are preferably designed to be as low and compact as possible to take the smallest headroom.
In the light of these somewhat conflicting design requirements that govern the efficiency and construction of intake systems, an improved intake system is disclosed in U.S. Pat. No. 4,708,097 entitled Induction System For V-Type Internal Combustion Engine issued on Nov. 24, 1987 and assigned to the same assignee as the present invention. The intake system taught by the U.S. Pat. No. 4,708,097 includes a surge tank arranged above one of first and second cylinder banks; first intake passages shaped in a C-configuration for feeding intake air from the surge tank to the cylinders in the first cylinder bank, each being connected with one side wall of the surge tank at one end and with one of the cylinders in the first cylinder bank at the other end and consisting of an upstream intake passage and a downstream passage; second intake passages shaped in an L-configuration for feeding intake air from the surge tank to the cylindners in the second cylinder bank, each being connected with the one side wall of the surge tank at one end and with one of the cylinders in the second cylinder bank and consisting of an upstream intake passage and a downstream intake passage. The first and second intake passages and are connected with the surge tank at different points in elevation. This intake system, although advantageous not only to reduce intake air resistance but to be constructed compact, still involves a problem to be solved because, in the case the intake system is subjected in particular to a stringent limitation of overall height, the surge tank has to be provided as a flattened surge tank which increases intake air resistance in a high speed operation range of engine.